1. Field of the Invention
This invention relates to a method for the production of a shaped hydrogel of absorbent resin and an apparatus for this production. More particularly, this invention relates to a method for the production of a shaped hydrogel of absorbent resin intended for the manufacture of an absorbent resin which exhibits high absorption capacity, little water-soluble content and little residual monomer , and enjoys high productivity.
2. Description of Related Art
In recent years, absorbent resins which are capable of absorbing some ten to some hundred times their own weights of water have been developed. Various absorbent resins have been finding utility in applications requiring absorption of water and retention of water as in the field of agriculture and horticulture, the field of fresh foodstuffs, and the field of industrial materials necessitating prevention of moisture condensation and heat insulation as well as the field of such sanitary materials as sanitary napkins and disposable diapers.
The absorbent resins of this class known to the public include a hydrolyzed starch-acrylonitrile graft polymer (JP-B-49-43,395), a neutralized starch-acrylic acid graft polymer (JP-A-51-125,468), a saponified vinyl acetate-acrylic ester copolymer (JP-A-52-14,689), a hydrolyzed acrylonitrile copolymer or acrylamide copolymer (JP-B53-15,959), products of cross-linkage thereof, a self-cross-linking sodium polyacrylate obtained by reversed-phase suspension polymerization (JP-A-53-46,389), and a cross-linked partially neutralized polyacrylic acid (JPA-55-48,304), for example.
Heretofore, the techniques represented by the aqueous solution polymerization have been known as methods for the production of an absorbent resin. As concrete examples of the techniques, a method which consists in subjecting the aqueous solution of a hydrophilic vinyl type monomer to adiabatic polymerization in a specific vessel (as published in JP-A-55-108,407, for example) and a method which consists in polymerizing a polymer gel while cutting it by agitation in a twin-arm kneader (as published in JP-A-57-34,101, for example) may be cited.
In the domain which resorts to the principle of applying a liquid reactant component in the form of a layer, at least 1 cm in thickness, on a movable endless revolving support belt and polymerizing the superposed layer, a method and apparatus for the continuous production of a polymer and a copolymer from a water-soluble monomer, characterized by introducing the liquid reactant component into a recess continuously formed from the support belt and, while the polymerization of the reactant component is in process, continuously transforming the recess of the support belt into an elongate flat belt, and continuously separating the formed polymer ribbon gel from the lateral end part toward the center of the recess formed of the support belt during the transformation of the recess formed by bending the support belt to the elongate flat belt has been proposed (JP-A62-156,102).
When the apparatus of this operating principle is adopted for a shaped hydrogel of absorbent resin intended to afford an absorbent resin, however, since the recess assumes a cross section of the shape of a bowl, the supplied liquid monomer mixture and the formed a shaped hydrogel of absorbent resin both assume a cross section of the shape of a bowl and induce a difference in thickness between the central part and the opposite edge parts, with the adverse result that the speed of cooling from the lower side will vary and the absorbent resin of uniform quality will be obtained only with difficulty.
An object of this invention, therefore, is to provide a method for the production of a shaped hydrogel of absorbent resin intended to afford an absorbent resin of uniform quality.
Another object of this invention is to provide a method for the production of a shaped hydrogel of absorbent resin intended to afford an absorbent resin which exhibits high absorption capacity, little water-soluble content and little residual monomer and enjoys high productivity.